Steering systems have a “steering ratio.” The steering ratio is defined as change in the steering output to the wheels or other traction elements of the vehicle with respect to change in the steering input from an operator of the vehicle. A larger steering ratio represents a steering system in which a relatively small steering input (e.g., rotation of a steering wheel, position change of a joystick) results in a relatively large change in the steered position of the steerable traction element(s) whereas a smaller steering ratio represents a steering system in which a relatively large steering input results in a relatively small change in the steered position of the steerable traction element(s).
In the case where the steering system has a steering wheel, the steering wheel will rotate a number of revolutions between a vehicle full-left turn and a vehicle full-right turn (i.e., “full steering articulation”). This number of revolutions is referred to herein as the number of “lock-to-lock turns,” the term “lock” referring to each stop (mechanical, electrically programmed, or otherwise) establishing the respective endpoint of the range of motion of the steerable traction element(s). It is to be understood that this number need not be a whole number as it may include some fraction of a revolution.
Some steering systems employ flow rate amplification, which may affect the steering ratio. Flow rate amplification may be represented qualitatively by a flow rate amplification ratio (Qamp) of a steering control unit of the steering system according to the equation: Qamp=Qactual(S×D), wherein Qactual is actual output flow rate of the steering control unit, S is actuation speed of a steering input device, and D is fluid displacement of a fluid meter. A larger flow amplification ratio results in a larger steering ratio and, in the case where the steering input device is a steering wheel, a smaller number of lock-to-lock turns, which may be useful during a “roading” mode in which the vehicle is traveling at higher speeds. On the other hand, a smaller flow amplification ratio results in a smaller steering ratio and, in the case where the steering input device is a steering wheel, a larger number of lock-to-lock turns, which may be useful during a “working” mode in which the vehicle is stationary or traveling at lower speeds.